"We were all young once," he tries to wave it away with a twirl of his hand and the expectation that everyone has done wild things in their youth that they're not particularly proud of. It's hardly the Doctor's fault that his youth happens to stretch for so long of a period. "And at the end of the day, we remained friends, so it's a happy ending! You see, and you never know when you need a friend to convert carbon dioxide to oxygen for you and I've got someone tucked away in the likely event."